Optical recording element

ABSTRACT

An optical recording element comprising a light-absorptive layer supported by a dimensionally stable substrate in which the light-absorptive material is a uniformly smooth, thin, homogeneous layer of film-forming polymeric dye having a light absorptivity of at least about 0.046 in the visible and/or infrared spectral regions.

This is a continuation of application Ser. No. 585,106, filed Mar. 1,1984, U.S. Pat. No. 4,581,317.

FIELD OF INVENTION

The invention is directed to an optical recording element and, inparticular, to such recording elements in which both the recording andplayback of data utilize laser beams.

BACKGROUND OF THE INVENTION

In response to the demand for more reliable and higher capacity datastorage and retrieval systems, there is considerable activity in theresearch and development of so-called optical disk recording systems.These systems utilize a highly focused modulated beam of light, such asa laser beam, which is directed onto a recording layer which is capableof absorbing a substantial amount of the light. The heat thusly producedcauses the light-absorbing material in the areas struck by the highlyfocused laser beam to change chemically and/or physically, thusproducing a concomitant change in optical properties, e.g.,transmissivity or reflectivity, in the affected area. For readout, thecontrast between the amount of light transmitted or reflected from theunaffected parts of the absorbing layer and from the marked areas of thelayer is measured. Examples of such recording systems are disclosed inU.S. Patents throughout the literature and in numerous U.S. Patents suchas U.S. Pat. Nos. 3,314,073 and 3,474,457. In recording data, a rotatingdisk having a light-absorptive recording layer is exposed to modulatedradiation from a laser source. This radiation is passed through amodulator and appropriate optics, and the highly focused laser beam isdirected onto the disk which forms by chemical and/or physical reactionof the light-absorbing layer a series of very small marks along acircular path within the light-absorptive layer. The frequency of themarks is determined by the modulator inputs. Using laser beams with afocused spot diameter of 1 μm or less, data can be stored at a densityof 10⁸ bits/cm² or higher.

The simplest optical disk medium consists merely of a dimensionallystable solid substrate on which is coated a thin layer oflight-absorptive material such as a metal layer. When thelight-absorptive layer is struck by an intense beam of coherent light,such as from a laser source, the light-absorptive material is eithervaporized and/or thermally degraded, thereby producing a very smallmarked area which exhibits different transmissivity or reflectivity thanthe adjacent unmarked layer. Multilayer antireflection structures, suchas those disclosed in U.S. Pat. No. 4,305,081 to Spong and U.S. Pat. No.4,270,132 to Bell, increase the absorption of the laser beam which alsogives better read/write contrast than with the use of simple singlelayer media. Therefore, for purposes of obtaining better powerefficiency, sensitivity and permanency of the record, it has beenpreferred to use multilayer antireflective structures.

There are two basic types of multilayer antireflective structures, oneof which is basically a bilayer structure and the other a trilayerstructure. In bilayer media, the substrate is coated with a very smooth,highly reflective material such as aluminum, on top of which is coated alayer of moderately light-absorptive material which is preferably of athickness corresponding to about λ/4n, where λ is the wavelength of therecording light source and n is the refractive index of thelight-absorptive layer. In trilayer media, the substrate is likewisecoated with a first layer of very smooth highly reflective material onwhich is coated a second layer of transparent material. Atop thetransparent second layer is coated a thin third layer of stronglylight-absorptive material. The combined thickness of the transparent andabsorptive layers is preferably adjusted to be about λ/4n. In both typesof structures, the adjustment of certain layer thicknesses according tothe wavelength of light and refractive index of the layer is for thepurpose of minimizing the amount of light reflected from the unmarkedareas and maximizing the amount of light reflected from the markedareas, thus producing a higher playback signal amplitude. A detaileddiscussion of the three types of disk construction is given by A. E.Bell in Computer Design. Jan. 1983, pp. 133-146 and the references citedtherein. See especially Bell and Spong, IEEE Journal of QuantumElectronics, Vol. QE-14, 1978, pp. 487-495.

It will be realized, of course, that the terms "bilayer" and "trilayer"refer only to the fundamental optical layers and do not exclude the useof ancillary layers. For example, a very thin layer of polymericmaterial may be interposed between the substrate and the reflectivelayer in order to compensate for insufficient smoothness of thesubstrate or to improve adhesion of the reflective layer. Also, one ormore transparent layers may be coated over the light-absorptive layer toprotect the fundamental layers from adhesive atmospheric conditions orto insulate thermally the other layers. Also, quite frequently thelight-absorptive layer will be coated with a relatively thick layer oftransparent material which serves as a defocusing layer which preventssurface dust and contaminants from interfering with the opticalproperties of the entire medium.

The desired properties of optical recording media are (1) highsensitivity, (2) high signal-to-noise ratio (SNR), (3) high tolerance tomaterial variation, contaminants and other defects, and (4) higharchival stability after extended storage and/or recording and readout(see Bartolini, J. Vac. Sci. Technology Vol. 18, No. 1, Jan./Feb. 1981,p. 70). Based upon these criteria, a considerable amount of research hasbeen and continues to be carried out directed to obtaining the bestpossible disk materials. In particular, a majority of the work done upto this time on materials for the light-absorptive or recording layerhas been directed to thin films of metals and chalcogenides such astellurium and tellurium alloys, rhodium, bismuth, indium, lead,aluminum, platinum, nickel, titanium and silver. Of these, by far thegreatest amount of work has been directed to the use of tellurium andits alloys with such elements as arsenic, antimony, selenium, germanium,phosphorus, silicon, thalium, indium, tin, copper, silver, iron,bismuth, aluminum, zinc and vanadium. Inorganic oxides such as leadoxide, tungsten oxide, titanium oxide, silicon oxide, zirconium oxideand the like have also been investigated and found to be suitable tosome extent as the recording medium for optical disks.

In addition, considerable effort has been directed to finding suitableorganic-based light-absorptive materials. These have been largelymetal/polymer composites or dye/polymer composites. In the former case,finely divided metal particles are dispersed in an organic polymermedium. In the latter case, a dye is dissolved in, or finely dividedpigment particles are dispersed in, an organic polymer medium.

The many issued patents which are directed to various dyes anddye/polymer dispersions are indicative of the high level of interest insuch materials. Several patents disclose the idea of using as anabsorptive medium a thin layer of deposited dye, e.g., U.S. Pat. Nos.4,023,185 4,097,895, 4,101,907, 4,190,843, 4,218,689, 4,219,826,4,241,355, 4,242,689 and 4,315,269. Other patents disclose the use ofdispersions of dye in an organic polymer medium. For example, U.S. Pat.No. 3,314,073 to Becker discloses the use of dyed gelatin or India inkand U.S. Pat. No. 4,360,908 to Howe et al. discloses the use of(dialkylaminobenzylidene) ketone dyes dispersed in a cellulose nitratebinder. In a similar manner, U.S. Pat. No. 3,723,121 to Hauser disclosesa process for laser beam recording using colored thermochromic materialswhich, when heated with the laser beam, change to a color whichtransmits the laser beam. The materials are used either by themselves ordispersed in finely divided form in a film-forming organic polymer suchas polyvinyl alcohol and/or gelatin.

In a different vein, U.S. Pat. No. 4,360,583 to Engler et al. isdirected to a process for duplicating an optical record by conventionalUV exposure through a photomask. The light-absorptive layer is a filmcomprising functionally substituted tetraheterofulvalene and liquidhalocarbon which co-react upon exposure to light. The photoreacted filmis then solvent developed to produce contrasting light-absorptive imageareas, which can be read by a laser beam.

Despite the great amount of research and development in this area oftechnology and the great number of materials tested, none of these hasexhibited the capability of being formed into optically suitable imaginglayers with both low cost of manufacture and with high performancereliability. In particular, the goals of economically achieving goodsensitivity, high signal-to-noise ratio and exceptionally smooth surfacecharacteristics have heretofore not been achieved.

BRIEF DESCRIPTION OF THE INVENTION

In its primary aspect, the invention is therefore directed to an opticalrecording element comprising a light-absorptive layer supported by adimensionally stable substrate in which the light-absorptive material isa uniformly smooth, thin, homogeneous layer of film-forming polymericdye having a light absorptivity of at least about 0.046 in the visibleand/or infrared spectral regions. As used herein, the term lightabsorptivity means the optical density of a film of one micrometerthickness.

DETAILED DESCRIPTION OF THE INVENTION A. Light-Absorptive Material

The light absorptive materials which are suitable as the active layer ofthe invention are film-forming polymers having chromophoric groups aspart of the polymer molecule, that is, polymeric dyes. Thus, thesematerials differ substantially from the prior art optical disk materialsin that, in this case, the chromophoric moieties are an integral part ofthe film-forming polymer--either as part of the polymer chain or pendentthereto--and not merely a dispersion of a dye compound or pigment in anorganic medium.

The following terms are used herein in accordance with the definitionsgiven in Hackh's Chemical Dictionary, 4th Edition, McGraw-Hill BookCompany, NY (1969):

"Auxochrome" is a radical that intensifies the color of a chromophore ordevelops a color from a chromogen.

"Bathocrome" is an organic radical which displaces the absorptionspectrum of an organic molecule toward the red.

"Chromogen" is a structural arrangement of atoms in many colored organicsubstances, e.g., -N=N-

"Thermal Diffusion Length" (l) is defined in U.S. Pat. No. 4,222,071 bythe relationship l=√kΥ, in which k is the thermal diffusivity of thelayer material and Υ is the exposure time. A thin layer of low thermaldiffusion length, i.e., having a diffusion length less than the diameterof focussed area of the recording beam, provides a highly sensitiverecording medium.

As used herein, the term "film-forming" means that the polymeric dye issolid or semi-solid at room temperature and is capable of being formedinto a coherent film by conventional coating or extrusion methods.

Polymers having chromophoric groups as part of the polymer molecules,i.e., polymeric dyes, can be made directly by both free radical andcondensation polymerization techniques or they can be made bypost-polymerization reaction of copolymers having pendent functionalgroups with reactive chromophoric materials in accordance with processeswhich are well known in the polymerization art. In the case of both freeradical polymers and post-polymerization reaction polymers, thechromophoric and/or chromogenic moiety is generally pendent to thepolymer chain, whereas in the condensation polymers, the chromophoricand/or chromogenic moiety is usually part of the polymer chain.

Condensation copolymers of the type which is suitable for use in theinvention are disclosed in copending U.S. patent applications Ser. No.514,890, filed July 18, 1983 and Ser. No. (PD-2015), filed concurrentlyherewith, which are incorporated herein by reference. These polymers areprepared by the condensation reaction in solvent medium of an aromaticpolyamine such as 4,4'-diaminodiphenylamine, or a salt thereof, withmalonaldehyde in the presence of a strong acid. As used herein, the term"polyamine" means an aromatic compound containing at least two reactiveamine groups. Chromophoric aromatic polyamines are preferred.

The polymeric dyes produced from this reaction contain a highlyconjugated polymethine-type chromophoric system as an integral part ofits backbone structure and can be represented by the formula: ##STR1##The polymethine-type structures referred to here may in some cases bereferred to as iminium or amidinium ion moieties. Such groups can befound in cyanine-type dyes.

Other polymeric dyes of this type include those prepared by thecondensation reaction of malonaldehyde with the following chromophoricpolyamines:

p-phenylenediamine

4,4'-diaminobenzophenone

Solvent Green 3

Direct Black 22

1,4-diaminoanthraquinone

New Methylene Blue N

Oil Blue N

Pararosaniline Base

Thionin

Acid Black 48

Cresyl Violet Acetate

3,6-diamino-9-fluorenone

4,4'-diaminodiphenylamine

Solvent Blue 59

N,N,N',N'-tetrakis(p-aminophenyl)-p-phenylenediamine

Acid Fuchsin

Acid Blue 161

Acid Blue 45

Acid Alizarin Violet N

Nigrosine

3,6-diaminoacridine

Substituted 6,6-diphenyl-6H-chromeno[4,3-b]indoles and carbonium ionsalts thereof

3,6-diamino-9-hydroxy fluorene analog of triphenylmethane

3,6-diamino-12-dimethylamino fluorene analog of triphenylmethane, HCl

Similar condensation polymers can be prepared by reacting suchpolyamines with diacid chlorides to produce the corresponding polyamidessuch as the following:

    ______________________________________                                        Polyamine          Diacid Chloride                                            ______________________________________                                        Thionin            Adipoyl chloride                                           Solvent Blue 59    Adipoyl chloride                                           Thionin            Sebacoyl chloride                                          Cresyl violet      Sebacoyl chloride                                          acetate                                                                       ______________________________________                                    

Reactions of this type can be represented by the following generalizedreaction: ##STR2##

Likewise a still further class of condensation polymer can be preparedby the reaction of such diacid chlorides with the correspondingdiphenols to produce the corresponding polyesters. Reaction of this typecan be represented by the following generalized reaction: ##STR3##

In addition, there are many ethylenically unsaturated monomeric dyeswhich are capable of undergoing free radical polymerization such as thefollowing: ##STR4## All of the above listed monomers produce polymers inwhich the chromophoric moieties are pendent to the polymer chain.

The preparation of polymeric dyes generally by copolycondensation and byfree radical-initiated copolymerization is described by E. Marechal inPure & Applied Chemistry, Vol. 52, 1980, pp. 1923-1928. See also E.Marechal, "Polymeric Dyes-Synthesis, Properties and Uses", Process inOrganic Coatings, 10 (1982), 251-287.

When any of the above-described polymeric dyes are used as thelight-absorptive material for the invention, several advantages areobtained: (1) the material is film forming and has substantialreflectivity; (2) very short imaging times are needed, e.g., ≦300 nsecand the polymer has low thermal diffusion length; (3) there is excellentcontrast between the image (marked) and nonimaged (unmarked) areas; (4)the polymer material is relatively quite inexpensive; (5) the polymercan be applied economically such as by spin-coating techniques; (6) thepolymer has good long-term stability and therefore would give permanenceof records; and, (7) especially in the case of the above-describedpolymers containing the amidinium-ion chromophoric system, the layerabsorbs a broad range of light in the visible and near infraredwavelengths.

A still further advantage of the invention is that the polymeric dyelight-absorptive material can be made with a wide range of lightabsorptivity in a variety of ways. For example, a polymeric dye of givenlight absorptivity can be diluted with an inert, transparent andcompatible polymer to whatever lower light absorption level may bedesired. Conversely, light absorption by the polymeric dye can beincreased in the same or in an expanded wavelength region by dispersingtherein additional colorants such as dyes or finely divided particles ofopaque solids such as carbon or metals which are completely inert towardthe polymeric dye at ambient conditions. In the case of those polymericdyes made by free radical polymerization and by post-polymerizationreaction, the degree of absorptivity can be adjusted by raising orlowering the amount of functional copolymers in the polymerizationreaction system. Similarly, in the case of polymers to which thechromophoric moieties are added by post-polymerization reactions, theconcentration of those moieties and the absorptivity can be adjusted byraising or lowering the degree of reaction with whatever pendentfunctional groups are present.

The polymeric dyes of the invention can be treated with oxidants such asAgAsF₆ to shift the absorptivity of the polymer salt to longerwavelengths of light. They can also be treated with electron acceptorssuch as tetracyanoethylene (TCNE) or tetracyanoquinodimethane (TCNQ) andits derivatives to give stable charge-transfer complexes which have asimilar shift in absorptivity. In particular, the TCNQ complexes exhibitintense absorption bands between 800 and 900 nm. Therefore, they areuseful with near-IR diode laser sources.

In all cases, it is preferred that the polymeric dye contain asufficient molar percentage of the chromophoric monomer to give theresultant polymer or copolymer a light absorption of at least about0.046 at the selected wavelength of laser irradiation. It will, however,be recognized by those skilled in the art that in some instances thechromophoricity of a selected reaction species may result afterincorporation in the polymer. That is, precursors of chromophoricmoieties may be used as well as those materials which are chromophoricbefore their incorporation into the polymeric molecule.

When the polymeric dye is struck by a coherent beam of light such as alaser beam of sufficient power, a distinct mark is produced in the areaof exposure. The mark may be the result of physical removal of thepolymer layer to form a pit. On the other hand, the mark may be theresult of chemical reaction since it is estimated that localtemperatures in the marked area may reach as high as 800° C. or higherfor quite short times on the order of only a few nanoseconds. Such amarking mechanism produces chemical changes which decrease the lightabsorptivity of the marked area and thus provides a readable contrastwith the amount of light absorbed by the nonaffected areas of the layer.Because of this duality of mechanism, it is not at all essential thatthe polymer dye be affected throughout the layer thickness or that theunderlying layer be exposed. In this regard, it is noted that therelative amount of chemical and/or physical change, e.g., byvaporization and thermal and chemical reactions may be affected by athermal insulation effect of the adjoining layers and the dye layeritself which tend to inhibit dissipation of the thermal energy from thelaser write beam. This effect may be expressed quantitatively as thethermal diffusion length. (See above). The precise mechanism of markformation, therefore, is highly variable as well as ambiguous.

B. Substrate

The substrate materials which can be used in the invention are thosewhich are dimensionally stable within the assembled structure. Thesubstrate can be either opaque or transparent and can be made ofvirtually any of the conventional substrate materials such as aluminum,glass, quartz, copper, brass, steel, magnesium, cadmium, silver, gold,polyester film, poly(tetrafluoroethylene) film, polyamide films, andother plastic or composite materials. In some cases, the polymeric dyeitself can be used as a substrate material. In addition, the substratemay be coated with a smooth layer of an adherent second material toprovide further surface uniformity and/or to act as a base for otherlayers to be deposited thereon. In all cases it will be recognized thatchemical inertness as well as dimensional stability over a prolongedperiod of time are essential properties of whatever substrate materialis chosen.

C. Optical Medium Construction

Though not limited thereto, the most highly preferred optical mediumconfiguration is a disk which typically has a diameter of 5-14 inches(12.5-35 cm). The optical recording elements of the invention can be ofeither single or multilayer construction. Thus, one or more layers ofother materials may be interposed between the polymeric dye layer andthe substrate and the polymeric dye layer may also be covered by one ormore ancillary layers.

A simple optical recording medium is comprised of a flat aluminum diskon which is directly coated a thin layer of the polymeric dye of theinvention which is reflective to the laser read beam. Although thereflectivity of the polymeric dye layer is less than the reflectivity ofa metal coating, it has been observed quite surprisingly that thesignal-to-noise ratio (SNR) of media using polymeric dye as theabsorptive layer is comparable to the SNR of more complex media havingmetallic reflective layers and conventional light absorptive materials.For this reason, such simple media using polymeric dyes are suitable formost commercial applications and have the additional advantage of beingmore economical to fabricate than conventional multilayer media. Forsome applications, the resulting element may be comprised solely of adisk formed from the polymeric dye, the thickness of the disk beingsufficiently greater than the depth of the laser write beam to givewhatever dimensional stability is required for the intended use andstorage conditions of the disk.

A more complex but practical medium is the bilayer disk which typicallyis comprised of a flat aluminum disk on which is coated a very thin andevenly coated polymer layer, e.g., acrylic polymer, to compensate forsurface irregularities on the aluminum disk. On top of the polymer layeris a thin layer of highly reflective metal, such as aluminum, silver,copper or alloys thereof, atop which is coated a thin layer of theabove-described light-absorptive polymeric dye. In this instance, thepolymeric dye may be diluted with a compatible transparent polymer toprovide the desired light absorption and layer thickness.

In turn, the polymeric dye layer may be protected with a thintransparent layer of inorganic or organic material to avoid eitherphysical or chemical damage in the recording or reflective layers. Thelayer, or layers, overlying the recording layer may also serve adefocusing function as well as a protective function.

The composition of the overlying layer(s) is not particularly critical,except that it should be inert with respect to the underlyinglight-absorptive layer. Physically the overlying layer should be atleast substantially transparent and preferably impermeable to ambientatmosphere and contaminants. Suitable materials for the overlying layersinclude polytetrafluoroethylene, polymethylmethacrylate,poly(vinylchloride), poly(ethylene terephthalate), silicon dioxide andthe like.

A further quite practical construction for the recording medium is thetrilayer disk. This construction utilizes the same layers andapplication procedures as the bilayer disk, but requires theinterposition of a layer of transparent material between the reflectiveand polymeric dye layers. The thickness of the interposed layers is thenadjusted to provide the necessary optical characteristics and to givethe medium the required degree of reflectivity.

In manufacturing the optical recording media of this invention, thevarious layers are formed by many different techniques depending inlarge part upon the surface precision which is needed. For example, apolymeric leveling layer can be formed by coating the substrate with athin solvent solution of the polymer and then removing the solvent byslow evaporation to avoid imperfections. Spin coating is especiallyeffective to obtain very thin coatings of uniform thickness. On theother hand, when very thin polymeric coatings are needed, especiallythose requiring optical smoothness, techniques such as plasma-phasepolymerization may be warranted. However, when relatively thick layersare permissible, preformed films can also be used, which are applied bylamination with heat and pressure. With respect to the reflective metallayer, however, sputtering and evaporation techniques are used to givemost reliable results.

The invention will be better understood by reference to the followingexamples:

EXAMPLES Example I--Polymeric Dye Synthesis A. Polymerization

The reaction to form the polymeric dye is a condensation between anaromatic diamine and 1,3-propanedialdehyde (malonaldehyde) which resultsin a highly conjugated polymethine-type chromophoric system, for exampleas follows: ##STR5## The absorption spectrum of the polymer can be tunedto the wavelength of the imaging and reading lasers by varying thestructure of the aromatic diamine. Polymers have absorption in thevisible and infrared wavelength regions have been prepared. The aromaticdiamines which have been used in this reaction are listed above in thediscussion of light-absorptive materials.

The reaction is carried out in dimethylsulfoxide (DMSO),N,N-dimethylformamide (DMF), 1-methyl-2-pyrrolidone (NMP) or a mixtureof these solvents, chosen because they appear to be the best solventsfor the polymer formed in the reaction. Allowing the product to remainin solution gives higher molecular weights. A few grains (1-25 g) of thearomatic diamine is dissolved in the solvent in a 500 ml resin kettlefitted with N₂ inlet and outlet and a Teflon® fluorocarbon resinstirring blade. After a thorough N₂ purge, the malonaldehyde (equimolarquantity) is added. The malonaldehyde is added as thebis(dimethylacetal) since malonaldehyde itself cannot be isolated. Theacetal (Aldrich, BP=183° C., n_(D) ²⁰ =1.4081, p=0.997, combustibleliquid) readily decomposes to the aldehyde in the presence of acid. Anequimolar equivalent of trifluoromethanesulfonic acid (CF₃ SO₃ H,Aldrich, BP 163° C., n_(D) ²⁰ =1.327, p=1.696, hygroscopic, corrosive)is added to the reaction mixture using a syringe after the malonaldehydehas mixed well into the solution. The resin kettle is immersed into asteam bath for 4-48 hours. The viscosity of the reaction mixturetypically increases as the reaction proceeds. In some cases, a highlygelatinous mixture is obtained. The quantity of solvent is chosen tomake up a 5-10% (by weight) reactants solution.

A second method has been used to control the release of malonaldehydefrom the acetal form during the course of the reaction. In this secondmethod, the aromatic diamine and acid are dissolved in a solvent(usually DMSO). Malonaldehyde bis(dimethylacetal) is dissolved in ˜50 mlsolvent and placed in a dropping funnel and this mixture was added tothe slurried, steam-heated reaction mixture over a period of ˜4 hours.The reaction was continued until polymerization occurred. In theExamples which follow, all of the polymeric dyes were made by one ofthese methods.

B. Purification

The most extensive studies have been carried out on the polymer (II),prepared from thionin (I) and malonaldehyde. ##STR6## Thus, thefollowing discussion refers to this thionin-containing polymer unlessotherwise noted.

Thionin was purchased from Aldrich Chemical Co. in the form of theacetate salt (94-97% purity). A chloride salt can be used but thepolymer formed is less soluble in dimethylsulfoxide. When thioninacetate is used in the polymerization, the reaction mixture forms agelatinous mass after ˜16 hours. An interesting property of this polymergel is that when it is exposed to the laboratory atmosphere (afterpolymerization under nitrogen), the gel rapidly liquifies. Apparentlythe dimethylsulfoxide absorbs enough water to reduce substantially themixture's viscosity. Gelation may be partly due to electrostaticinteraction between the charged polymer chains and therefore water mayinterrupt this interaction. The film-forming characteristics of theproduct were tested by placing a few drops of the reaction mixture on aglass slide and removing the solvent by heating slowly on a hotplate. Ahighly reflective film with a brownish sheen was obtained. The film wasbrittle but had good adhesion to glass. Films stored in an oven (˜125°C.) for several months showed no noticeable loss of reflectance orphysical properties.

The product contained water-soluble impurities, which were easilyleached from the polymer by soaking in water at room temperature. Thepolymer was purified by precipitation in distilled water. A quantity ofthe reaction mixture (in DMSO) was poured into an excess of distilledwater, while mixing in a Waring blender. The solids were suctionfiltered, reblended and filtered again. This procedure was repeateduntil the filtrate was clean. After air drying, the solids, thoughreadily soluble in conc. H₂ SO₄, did not rapidly redissolve in DMSO.Significant redissolution required prolonged periods of milling indilute solution. After all the solids redissolved, e.g. about 4-6 weekswith stirring, the solution was filtered through a 0.2 μmtransverse-flow polypropylene filter in preparation for film casting.Difficulties in redissolution are attributed to polymer crosslinking,which may be reduced substantially by avoiding polymer dry-down.

Example II Film Coating A. Film Casting for Laser Imaging

Films were cast from purified and unpurified polymer solutions indimethylsulfoxide by spin coating onto 2-inch by 3-inch glass slides.Film thicknesses were easily varied from fractions of a micron toseveral microns by adjusting the coating solution viscosity (≦˜15 Poise)and spinning rate. A Headway Research, Inc., Model EC101-CB15photoresist spinner was used for all spin coating operations. The moreviscous solutions required up to 3000 rpm to obtain a uniform filmgreater than 1 micron thick. Heat from an infrared (IR) lamp removedsolvent from the film while spinning.

B. Laser Marking of Polymer Films

Samples were prepared for laser imaging by spin coating a small portionof a DMSO/polymer solution onto glass microscope slides (2 inch×3 inch×1mm). Polymer solutions with viscosities between 5-15 Poise gaveapproximately 1 μm thick films at 2000-3000 rpm. Films on glass slideswere tested for imaging, sensitivity and readout capability using pulsedAr⁺ (488 nm) and HeNe (633 nm) lasers capable of delivering up to 33 mWand 5 mW, respectively, to a sample surface. Samples were mounted on acomputer-driven X-Y translation table and moved at a speed of 400microns/second beneath an incoming laser pulse train (variable up to 100μsec pulses; spaced ˜10 msec apart) which produced a linear array ofmarks (typically pits). Readout was accomplished using reduced power(≦0.8 mW) at the writing wavelength. The marks were detected by adecrease in light intensity reflected back to a photodetector.Reflectance of the polymer film surface ranged from 5-18% and thereflectance in the imaged area ranged from 0.5%.

Typical results for several polymers are summarized in Table 1 below:

                  TABLE 1                                                         ______________________________________                                        Laser Marking of Polymeric Dye Films                                                                    Minimum Laser                                                                 Pulse Width for                                     Polymer        %          Detection of                                                                            Write                                     Absorp-        Reflect. at                                                                              Image Using                                                                             Laser Power                               tivity Laser   Laser Wave Opt. Micro-                                                                             at Sample                                 (λmax)                                                                        Type    Length.sup.1                                                                             scope (800X)                                                                            Surface                                   ______________________________________                                        400 nm HeNe    15%        10 μsec                                                                              3.5 mW                                    (633 nm)                                                                       ##STR7##                                                                     490    HeNe    18%         1 μsec                                                                              3.5 mW                                     ##STR8##                                                                     550    HeNe    12%        700 nsec  2-5 mW                                     ##STR9##                                                                     630 nm HeNe    15%        300 nsec  2.5 mW                                     ##STR10##                                                                    630 nm Ar.sup.+                                                                              15%        50 nsec   33 mW                                     (488 nm)                                                                       ##STR11##                                                                    ______________________________________                                         .sup.1 633 nm for HeNe; 488 nm for Ar.sup.+-                             

Imaging sensitivity was very reproducible. Readout of image samples wasaccomplished by rescanning a line or array of pits with laser powerreduced to 100-800μ watt. The signal from the reflected light gatheredby a photodetector was displayed on an oscilloscope and printed out onan X-Y recorder. Even short pulse widths gave good contrast between theunimaged background and imaged pit. Readout response was also veryreproducible from one sample to another.

Stability of imaged samples was tested on a hot-stage microscope byfocusing on a sequence of pits at room temperature and then examiningthe pits at various temperatures at a heating rate of 5° C./min. Thepits remained clearly visible and apparently unharmed as the sample washeated to 250° C. and then cooled back down to room temperature. Theonly noticeable effect of the heat treatment was sublimation of somematerial on the sample surface as the temperature was elevated. Thismaterial is believed to have been unreacted aromatic diamine. However,at 250° C., this sublimation ceased. Nevertheless, the sample was stillhighly reflective after the heat treatment.

Example III Preparation of Polyamide Dye

2.00 g of thionin acetate (7.0 mmole), 1.82 ml triethylamine (14.0mmole) and 1.40 ml of sebacoyl chloride (7.0 mole) were added to 100 mlof 1-methyl-2-pyrrolidinone in a 250 ml Erlenmeyer flask fitted with adrying tube. The solution was stirred at 72° C. for 4 hours. Thesolution thickened as the reaction proceeded. A small volume of thereaction solution was evaporated onto a glass slide on a hot plate. Ashiny film resulted.

EXAMPLE IV Preferred Optical Disk Construction

A clean 14-inch O.D.×65/8-inch I.D.×˜2 mm thick aluminum disk is placedon a Headway Research Model LS 510 spin coater with an automaticdispenser arm. A solution is prepared comprising an acrylicpolymer.sup.(1) in 1 mol % aqueous NH₄ OH containing zinc acetate (2:1MAA:Zn acetate, molar basis). The solution having a viscosity of about200 cp is filtered through a 0.2 μm polypropylene filter and isdeposited on the disk at ˜30-50 rpm. The entire surface of the disc iscovered with the acrylic polymer solution. The disk is then spun rapidlyto ˜400-1000 rpm. Excess acrylic polymer solution is thrown off the disksurface leaving behind a uniform solution layer. Most of the water andammonia is removed from the layer during the 400-1000 rpm spin step.Residual solvent and ammonia is removed in a 125° C. oven. A uniformfilm approximately 4 μm thick is obtained after dry down. Because thebare aluminum layer is not smooth enough to coat thereon uniformlyultrathin (<1 μm) coatings, the acrylic layer serves as a smoothinglayer. It also serves as an adhesion promoting layer.

After drying, the aluminum disk with its smoothing layer is placed backon the spin coater. A solution of polymeric dye in dimethylsulfoxide(filtered through 0.2 μm pore polypropylene filter and having Brookfieldviscosity between 5 centipoise and 200 centipoise) is deposited on therotating disk at ˜30-50 rpm. The entire surface of the disk is coveredwith the polymeric dye solution. Preferred polymeric dyes are thoseprepared from the following monomers (condensation polymerizations):

(1) thionin+malonaldehyde bis(dimethylacetal) (Ar⁺ laser-sensitive),

(2) N,N,N',N'-tetrakis-(p-aminophenyl)-p-phenylenediamine+malonaldehydebis(dimethylacetal) (Ar⁺ laser-sensitive), and

(3) N,N,N',N'-tetrakis-(p-aminophenyl)-p-phenylenediamine+malonaldehydebis(dimethylacetal) oxidized with silver hexafluoroarsenate (diodelaser-sensitive).

(4) N,N,N',N'-tetrakis-(p-aminophenyl)-p-phenylenediamine+malonaldehydebis(dimethylacetal)+7,7,8,8-tetracyanoquinodimethane (TCNQ) (diodelaser-sensitive).

The rotation of the disk is increased to 300-1000 rpm. The excesspolymeric dye solution is thrown off the disk leaving behind a uniform,smooth solution layer. The dimethylsulfoxide is evaporated from thelayer by heating under an infrared lamp while the disk is spinning.Residual solvent is removed by further heating in a 100° C. oven.Polymeric dye films having thicknesses from 100 Å to 1 μm are coated.

The aluminum disk with smoothing layer and polymeric dye active layer isagain placed back on the spin coater. A solution of an organosilane(filtered through 0.2-μm pore polypropylene filter; Brookfield viscosity˜10-100 centipoise), e.g., General Electric RTV 6159, RTV 615, RTV 670or RTV 655, is deposited on the disk which is rotating at ˜30-50 rpm.The rotation of the disk is increased to 500-1500 rpm. Excess silanesolution is thrown off the disk leaving behind a smooth, uniformsolution layer. The silane is cured by heating in a 100° C. oven. Aflexible layer ˜500 Å-1 μm thick is obtained.

A 7-mil±0.5 mil poly(methylmethacrylate) dust defocusing layer is eitherlaminated to the disk containing smoothing, active and flexible layers(with the aid of an adhesive layer) or a UV-curable film (7 mil thick)is laminated to the disk (with the aid of an adhesive layer) and exposedwith a UV source to form a dust defocusing layer. The completed disk maybe stored in a cassette when not in use.

I claim:
 1. An optical recording element comprising a light-absorptivelayer supported by a dimensionally stable substrate in which thelight-absorptive material is a uniformly smooth, thin, homogeneous layercomprising a film-forming polymeric dye diluted with an inert,transparent and compatible polymer to lower the light absorption levelthereof, said light-absorptive material having a light absorptivity ofat least 0.046 in the visible and/or infrared spectral regions.
 2. Anoptical recording element having bilayer configuration comprising alight-absorptive layer supported by a dimensionally stable substrate inwhich the light-absorptive material is a uniformly smooth, thin,homogeneous layer comprising a film-forming polymeric dye diluted withan inert, transparent and compatible polymer to lower the lightabsorption level thereof, said light-absorptive material having a lightabsorptivity of at least 0.046 in the visible and/or infrared spectralregions.